EGR (exhaust gas recirculation) is used in automotive vehicle internal combustion engines for exhaust emission control. One type of EGR valve is vacuum operated, being controlled by vacuum delivered from an EVR (electric vacuum regulator) valve. The latter valve is controlled by the engine ECU (electronic control unit) to provide the appropriate amount of vacuum to the EGR valve. The EVR valve inlet port is communicated to engine manifold vacuum, and its outlet port to the vacuum inlet port of the EGR valve.
Intake manifold vacuum is not constant, but can vary significantly as the engine is operated. During periods of low intake manifold vacuum, the EVR valve is unable to maintain adequate levels of vacuum for proper control of the EGR valve, and as a consequence, emission infractions may occur.
The present invention relates to a vacuum sustaining valve that maintains a slowly declining vacuum input to the EGR valve during such periods of low manifold vacuum toward the objective of avoiding such infractions. If low manifold vacuum persists for an extended time, the vacuum sustaining valve will eventually bleed off to atmosphere the vacuum input to the EGR valve, shutting down EGR operation altogether.
The foregoing, along with further features, advantages, and benefits of the invention, will be seen in the ensuing description and claims, which are accompanied by a drawing. The drawing discloses a presently preferred embodiment of the invention according to the best mode contemplated at this time for carrying out the invention.